The present invention relates generally to improvements to bar code scanners. More particularly, the invention relates to advantageous techniques for designing and arranging optical components within a scanner so as to make efficient use of space and the use of space to arrange components so as to generate scan beams having a relatively long optical path length given space constraints imposed by a desired size for a scanner.
Detecting and decoding of bar codes by a bar code scanner is accomplished by detection of light reflected into the bar code scanner as a scan pattern strikes and is reflected from the bar code. The scan pattern typically comprises a plurality of scan lines,.with each scan line being traced out by the motion of a scan beam emitted from the scanner. The scan beam is typically generated by a reflection of a laser beam from a facet of a rotating spinner. After the initial reflection from the spinner, the scan beam is directed to and reflected from each mirror in a succession of fixed mirrors in order to give the scan beam a desired optical path length and to direct the scan beam through a scan window. As the spinner rotates, the laser beam experiences a relative motion across each facet of the spinner. The movement of the laser beam across each spinner facet causes the scan beam to move so as to trace out a scan line. The length of each scan line is related to the optical path length of the scan beam, and the total length of all scan lines produced by a revolution of the spinner increases as the optical path length of the scan beams increases.
The performance of a bar code scanner, that is, the efficiency and accuracy of detection and decoding of bar codes, improves as total scan line length increases. A longer total scan line length provides a greater amount of light per unit of surface area when scan lines strike a surface, and also provides a greater area of coverage. It is therefore highly desirable to generate scan beams having optical path lengths that are as long as possible given the physical and other constraints imposed by the design of the scanner, so that a long total scan line length can be produced.
Many popular scanner implementations impose relatively stringent size constraints on a scanner. Single window scanners, for example, arc typically relatively small, with an extremely popular and widely used size for single window scanners being approximately 6 by 6 by 3 inches. Repeated reflection of the scan beam by a sequence of fixed mirrors increases the optical length of the scan beam. However, the components required to generate, detect and process a scan pattern limit the space available for fixed mirrors and for travel of the scan beam. In a relatively small single window scanner employing prior art techniques, the scan beam typically experiences no more than two reflections after leaving the spinner and before arriving at the scan window. Increasing the number of reflections experienced by the scan beam, and providing unobstructed paths between reflections, would significantly increase the effective length of the scan beam. There exists, therefore, a need for a single window scanner having components designed and arranged so as to produce relatively long scan beams within the space constraints imposed by a relatively small size for the scanner. The space constraints imposed by the need to conform a scanner to a particular set of external dimensions, coupled with the space requirements imposed by prior art design techniques, present additional limitations that could be overcome by more efficient use of space in scanner design.
The present invention provides for efficient use of space within the scanner by employing a design for the rotating spinner within the scanner such that open space is available within the volume bounded by the spinner, and disposing a fixed mirror in the open space bounded by the spinner. The spinner includes a polygonal reflector, having reflective interior surfaces and being hollow and open at the top, and a motor to rotate the reflector. The collector mirror, used to deflect a laser beam to a facet of the spinner as well as to collect and focus diffuse light entering the scanner, is supported from a sidewall of the scanner and suspended within the space bounded by the hollow reflector. The placement of the collector mirror within the volume bounded by the reflector avoids the necessity of placing the mirror elsewhere within the scanner and makes space available for placement of other components within the scanner.
The placement of the collector mirror within the space bounded by the spinner makes it possible to implement arrangements of fixed mirrors within the scanner so as to provide a relatively long optical path for scan beams reflected from the spinner. In one preferred embodiment, a collection of fixed mirrors is designed and arranged within the scanner so that a scan beam produced by a reflection of the laser beam from the spinner reflector is directed along a path involving three or more changes of direction due to reflection. With unobstructed space for travel between reflections, the scan beam can be directed so as to travel through a longer total path than would normally be traveled by a scan beam that was reflected two or fewer times within the space constraints imposed by prior art designs. Because the scan beams are longer, the total length of the scan lines produced by the tracing out of the scan beams through a rotation of the spinner is longer.
The use of space within the volume enclosed by the spinner also allows alternative arrangements of components. For example, additional electronic components may be placed in the scanner that could not be easily included without the additional space. As another example, configurations of mirrors may be designed that allow the generation of scan beams emerging from the scanner at different angles than would be possible if the additional space were not available.
A more complete understanding of the present invention, as well as further features and advantages of the invention, will be apparent from the following Detailed Description and the accompanying drawings.